1. Summary of the Invention
The invention relates to a process for an addition reaction of silanes or siloxanes which have SiH groups with compounds having olefinic double bonds in the presence of a dissolved platinum(0) complex catalyst and with an activating amount of at least one unsaturated hydrocarbon.
2. Description of the Art
SiC-linked, organomodified siloxanes, especially polyethersiloxanes, with their widely adjustable surfactant behavior, constitute a class of substances which is very important industrially. The established method for the preparation of these substances is the platinum metal-catalyzed addition reaction of siloxanes and silanes having SiH groups with olefinically functionalized compounds, such as, for example, with allylpolyethers.
The use of platinum catalysts for the addition reaction of silanes or siloxanes having SiH groups with compounds having one or more olefinic double bonds is known (hydrosilylation) and is described, for example, in the book “Chemie und Technologie der Silicone [Chemistry and technology of the silicones]”, Verlag Chemie, 1960, page 43, and in the patent literature, for example in DE-A-26 46 726, EP-A-0 075 703 and U.S. Pat. No. 3,775,452. In present-day industrial practice, predominantly hexachloroplatinic acid and cis-diammineplatinum(II) chloride have become established.
Although this reaction principle is simple to describe, it is often complicated to carry out in a reproducible manner on an industrial scale.
On the one hand, this addition reaction takes place without significant formation of byproducts only when the compounds which have olefinic double bonds are free of groups which can react with the SiH group in competition with the addition reaction. In particular, the hydroxyl group bonded to carbon is to be included among these.
On the other hand, the required amounts of platinum metal in parts by weight per million parts by weight of the hydrosilylation mixture in order to obtain usable results are frequently so high that these processes are of no commercial interest.
In particular, however, poor SiH conversions lead to an undesired increase in molecular weight owing to the formation of new SiOSi bonds. As a consequence of this crosslinking, the viscosity of these products cannot be kept in the specified ranges.
Even active catalyst systems, such as, for example, those of the Karstedt type (U.S. Pat. No. 3,814,730), tend toward deactivation and cut-out phenomena in the preparation of organomodified siloxanes, in particular of allylpolyethersiloxanes, so that subsequent catalysis and/or also the drastic temperature increase in the addition reaction are often necessary.
In some cases, it is also found that it is disadvantageous for the hydrosilylation if the known platinum catalysts are used above the normal amounts by weight of catalyst and/or at high temperatures. As a result of these harsher reaction conditions, the formation of rearranged byproducts is forced.
WO-A-98/00463 describes defined solid compounds having high decomposition temperatures (144.3° C. and 138.4° C.), which, starting from the Karstedt catalyst and with addition of selected electron-poor olefins, are said to be an active and at the same time stable catalyst system for homogeneous hydrosilylation. The increased activity is attributed to the introduction of strong π-acid ligands, such as in particular methylnaphthoquinone or tetraethyltetracarboxylatoethylene.
In the examples mentioned, triethylsilane is subjected to an addition reaction with vinyltrimethylsilane, the olefin component being used in 100% excess. In spite of this large excess and taking into account the fact that the vinyl group, in contrast to the allyl group, does not have isomerization activity, the catalyst switches off here with deactivation at 50° C. after 2 hours, the SiH conversion reaching only 68%. At 73° C., this catalyst system decomposes immediately and leads only to 18% SiH conversion (P Steffanut et al., Chem. Eur. J. 1998, 4, No. 10, page 2014).
All measures mentioned at the outset for increasing the SiH conversion have to date had only an adverse effect on the achievable product quality with regard to sensory and technical properties.
The practical usability of products which arise from the platinum metal-catalyzed addition reaction of siloxanes carrying SiH groups with compounds having olefinic double bonds is in particular directly linked to the conversion achieved in the hydrosilylation, i.e. the minimization of residual SiH functions. Residual SiH leads to uncontrollable hydrolysis and crosslinking processes which, particularly in the case of addition compounds, of high molecular weight, lead to gelling and make the products unusable.
There has been no lack of efforts in practice, particularly in the case of the alkylsiloxane/polyethersiloxane copolymers which are used as emulsifiers and are prepared in a three-stage addition reaction, to trap residual SiH functions by treating the reaction matrix with excess ethylene as an SiH-binding auxiliary olefin. However, this measure does not have the desired efficiency, so that from about 2 to 3% of unconverted silicon hydrogen (based on the starting siloxane) remain. Experience has shown that such a product does not have a long shelf life and suffers gelling.
Particularly sensitive indicators for deviations from the quality level are, for example, those allylpolyethersiloxanes which are used as foam stabilizers in the preparation of flexible PU foams. As performance characteristics, the activity and the fineness of the cells are criteria for assessing the stabilizer quality. Process changes in the stabilizer preparation, such as, for example, the change of the catalysis conditions during the SiC linkage reaction, influence the foam quality.
There is therefore a need for a catalyst which overcomes the disadvantages of the prior art and, on the one hand, has high activity with respect to the addition reaction of the SiH groups at olefinic double bonds and, on the other hand, leads to few secondary reactions, in addition to the abovementioned rearrangement reaction it also being intended to avoid competing reactions in the form of the reaction of the SiH groups with OH groups of the polyethers and also disproportionation reactions within the silane or siloxane compounds used. This is to be understood as meaning a redistribution of the SiH groups in the silane or siloxane usually present in the mixture. A technical problem to be solved is defined in particular as also being able to carry out the SiC linkage reaction at low temperatures as quantitatively as possible and in a reliably stable manner, also in conventional steel reactors.
Surprisingly, it has now been found that all difficulties discussed at the outset and familiar to a person skilled in the art in the case of the SiC linkage reaction can be eliminated if the auxiliary olefins are added to the reaction mixture not after the end of the addition reaction but before the addition of platinum(0) complex catalyst solutions, in particular commercially available Karstedt complexes, these are treated with effective amounts of activating C2-6-Olefins and are added to the reaction mixture, and the hydrosilylation is carried out at moderate temperatures, preferably from about 20° C. to about 150° C., but in particular below about 60° C. A highly active platinum catalyst which can be safely handled and results in a quantitative SiH conversion in the desired reaction without further additional measures is thus obtained.